I think there is a typo in the answer as it describes query number 2 in the answer but mentions a WHERE clause which only exists in Query number 3. It mentions Query number 1 and mentions it uses a CTE, which is used in Query number 2.
The correct answer is query 2; the answer just incorrectly mentions query 2 as not running instead of query 3 as not running and that query 1 is the answer when query 2 is the answer.
The above is all just my opinion on what you should do.
As with all advice you find on a random internet forum - you shouldn't blindly follow it. Always test on a test server to see if there is negative side effects before making changes to live!